The effectiveness of a drug regimen is often highly dependent on achieving the necessary bioavailability of the drug once it is administered. Poor bioavailability of a drug makes it necessary to administer higher doses in order to achieve efficacy, but higher dosage requirements can lead to toxicity, undesirable side effects, and/or decreased patient compliance. Although the gastrointestinal tract is a common route for drug delivery, not all drugs are well absorbed through the lining of the gastrointestinal tract. In the case of some drugs, their polar nature or hydrophilic character may make them difficult to be absorbed. For example, drugs of high molecular weight molecules are difficult to successfully administer orally, because the acidic conditions and high enzymatic activity in the stomach can degrade such drugs. Delivering drugs through other routes, such as buccal, sublingual, rectal, nasal, vaginal mucosa, is one way to provide systemic access for drugs while avoiding the hostile environment of the gastrointestinal tract. However, for this to be successful, the drug administered must overcome the resistance of these membranes to absorption. It is therefore clear that any factor that enhances the rate of absorption through such surfaces will result in improved clinical efficacy of many drug therapies.
Early efforts to enhance the absorption, and therefore bioavailability, of drugs include the use of adjuvants, such as surface active agents, including ionic and non-ionic surfactants to increase biomembrane permeability. However, use of some adjuvants is attended by the risk of damaging the biomembrane. Therefore, a need continues to exist for compositions that safely promote the absorption of poorly absorbed drugs.